The present invention relates generally to an apparatus and method for arrangement of light beams, and more particularly, to an apparatus and method for switching an optical path.
Optical switches are basic and important elements in optical systems, especially in fiber optic communication systems. In a fiber optic communication system, an optical switch is employed to connect and disconnect the transmission path of an optical signal to route the light beam carrying information. In other optical systems optical switches are used to control the output of light sources. Due to the fast propagation of light, an optical switch should have a high switching rate for the operation of an optical system. Insertion loss is another main factor affecting the performance of an optical switch, and low insertion loss reduces the signal attenuation caused by the optical switch. An optical amplifier is added to increase the intensity of the optical signal when it is attenuated, and the insertion loss can be reduced by reducing the number of inserted optical elements and increasing the optical alignment accuracy. Optical misalignment might occur with an optical switch after it is repeatedly switched and thus significantly reduce the coupling rate of the optical signal switched by the optical switch. Therefore, stability is also very important for an optical switch.
A mechanic optical switch is a simple and cheap implementation theoretically; however, it suffers limitation. For instance, the optical switch and apparatus proposed by U.S. Pat. No. 6,044,186 issued to Chang et al. attaches the input optical fiber of an optical signal onto a switching member pivoting between two positions for the input optical fiber to be aligned with different output optical fibers in order to switch the optical signal. It is necessary for such approach to move the optical fiber, therefore, a very high accurate alignment is required and the reliability is low.
It is simpler and better to change an optical path by an optical element instead of by moving the optical fiber. Reflection type optical switches are proposed, such as by U.S. Pat. No. 5,838,847 issued to Pan et al., which place and remove a movable reflective device at the end of an optical fiber to change the optical path. However, the reflective device is too sensitive to angular variation to switch fast and accurately, and there are some optical switches that cannot be implemented with this technique.
In U.S. Pat. No. 6,088,166, Lee can parallel move a light beam from one optical fiber to another by a prism, with which the light beam is reflected twice by the prism. Although that is a simple and cheap implementation, the prism that serves as the optical switching element is too huge and heavy to reduce the size of the apparatus and as a result, it is disadvantageous to design the mechanism to operate the prism and to implement an apparatus with more inputs/outputs (I/O). In U.S. Pat. No. 6,215,919, Li et al. redirect a light beam by a wedge prism in combination with a suitably positioned gradient index lens in order to switch the light beam from one optical fiber to another. Although this approach can reduce the size and weight of the required prism, the control of the optical path becomes complicated and thus a highly precise prism and accurate optical alignment are necessary. In addition, it is difficult to achieve multiple I/O for an optical switch.
It is therefore desired to provide a simple, cheap, light and stable apparatus and method for switching an optical path.
One object of the present invention is an apparatus and method to change an optical path, by which different optical paths can be switched in order to control the propagation path of a light beam.
Another object of the present invention is an apparatus and method to change an optical path, by which the optical path is switched without moving the input or output of any optical fiber or signal.
Yet another object of the present invention is to disclose a small and light apparatus for switching an optical path.
Still another object of the present invention is to teach a simple and cheap apparatus and method for arrangement of an optical path.
According to the present invention, an apparatus and method for switching an optical path comprises one or more I/O of optical signals arranged to form a free-space optical path between the I/O, and a prism movable to the free-space optical path being inserted into or removed from the free-space optical path to control the propagation path of a light beam between the I/O.
When the prism is inserted into the free-space optical path, a switched optical path between the I/O is formed, the light beam from the input to the corresponding output is thus refracted twice and totally reflected once by the prism. When the prism is removed from the free-space optical path, the light beam propagates from the input to the output along the free-space optical path.
Preferably, the prism is a dove prism or an isosceles prism to reduce the size and weight of the optical switch apparatus.
The present invention can be applied to various types of optical switch apparatus, such as 1xc3x972 optical switch, 2xc3x971 optical switch, 2xc3x972 optical switch, 2xc3x972 blocking type optical switch, and on-off optical switch, even an optical switch with multiple I/O by stacked prisms, such as 1xc3x974 optical switch and 2xc3x974 optical switch.